Proxy active scan for wireless networks

ABSTRACT

Active scanning method in a wireless network for fast determining available access points ( 106, 806 ) using inter-AP (Access Point) communication is described. In the scanning method, a mobile station ( 102, 802 ) sends Probe Request for Proxy frame to the current AP ( 104, 804 ) serving the mobile station ( 102, 802 ). In response to the Probe Request for Proxy frame, the current AP ( 104, 804 ) send Proxy Probe Request packet to the appropriate APs ( 106, 806 ). In response to the Proxy Probe Request packet, the neighbor APs ( 106, 806 ) send Probe Response frame to the mobile station ( 102, 802 ) on its operating channel. Since the mobile station ( 102, 802 ) moves to the channel being examined after sending the Probe Request for Proxy frame, it receives the Probe Response frame if it is in the coverage area of the neighbor AP ( 106, 806 ). The content of Probe Response frame provides the mobile station ( 102, 802 ) with the information to be used in handoff decision and network join procedures. Thus, the mobile station ( 102, 802 ) neither has to move to the channel to be examined nor send Probe Request frame on that channel. This enables active scan to be initiated even when the neighbor AP ( 106, 806 ) is operating in PCF (Point Coordination Function) and the network is in CFP (Contention Free Period), during which unassociated mobile stations (including the scanning mobile station) cannot send packets.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/479,124, filed Jun. 13, 2003.

BACKGROUND

1. Field of the Invention

The present invention relates generally to wireless networks, and moreparticularly to scanning and establishing communications in a wirelesslocal area network.

2. Related Art

In order for a mobile station to determine which network to join, themobile station must first scan for available networks. Scanning can bepassive or active. Passive scanning involves listening for beacon framesfrom APs (access points). Active scanning, on the other hand, involvesthe transmission of Probe Request frames for soliciting a Probe Responseframe from access points in the area. Receiving a beacon frame (passivescanning) or a Probe Response frame (active scanning) from an accesspoint allows the mobile station to learn the availability and/or thecharacteristics of the network that is coordinated by the access point.Scanning, either passive or active, can take place on one or more radiochannels according to the number of radio channels available for thewireless network.

One of the significant problems of the conventional scanning methods isthat they are not fast enough to prevent communication interruptionduring handoff. In case of IEEE 802.11 Wireless LAN, an empiricalanalysis of handoff process found that active scanning may have highlatency of as much as 50 msec per channel. Details can be found in IEEE802 Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer(PHY) specifications, IEEE Standard 802.11, 1999 and “An EmpiricalAnalysis of the IEEE 802.11 MAC Layer Handoff Process,” by AruneshMishra, Minho Shin, William Arbaugh, submitted to ACM CCR, both of whichare incorporated by reference in their entirety. Passive scanning inIEEE 802.11 has an even higher latency since the mobile station muststay on each channel for at least one beacon interval, whose recommendedvalue is 100 msec. A more detailed description can be found in MatthewS. Gast, “802.11 Wireless Networks—The Definitive Guide,” O'Reilly,April 2002, which is incorporated by reference in its entirety. Largescanning time may contribute to TCP timeout, triggering TCP congestionavoidance algorithm, which results in decreased throughput. The largescanning time may also seriously deteriorate quality of voice service,since the maximum interruption time allowed for voice application is 50msec (ideally, interruption time should be kept less than 35 msec).

This situation will be more aggravated if PCF (Point CoordinationFunction) is used in the APs to be scanned. If an AP is operating PCF,only an associated mobile station has the right to be added to thepolling list, and during a CFP (Contention Free Period) only the mobilestation in the polling list may access the wireless medium if polled bythe AP. Since a mobile station in active scanning is not associated withthe APs to be scanned, the mobile station cannot send Probe Requestframes during the CFP. As a result, scanning latency is dramaticallyincreased.

Therefore, a scanning method for wireless networks that has smallerlatency is desired.

SUMMARY

In accordance with one aspect of the present invention, an activescanning method in a wireless network uses inter-AP (Access Point)communication for fast determining the available access points for amobile station. In the scanning method, the mobile station sends a ProbeRequest for Proxy frame to the current AP serving the mobile station. Inresponse to the Probe Request for Proxy frame, the current AP sends aProxy Probe Request packet to the appropriate neighboring APs. Inresponse to the Proxy Probe Request packet, the neighboring APs sendProbe Response frames to the mobile station on its operating channel.Since the mobile station moves to the channel being examined aftersending the Probe Request for Proxy frame, it receives the ProbeResponse frame if it is in the coverage area of the neighboring AP. Thecontent of Probe Response frame provides the mobile station with theinformation to be used in handoff decision and network join procedures.Thus, communication between the mobile station and a neighboring AP isfrom the mobile station to the current AP to the neighboring AP to themobile station, as opposed to Probe Request and Probe Response sentdirectly between the mobile station and neighboring AP as withconventional methods.

One advantage of the present invention is that the mobile stationneither has to move to the channel to be examined nor has to send aProbe Request frame on that channel. This enables active scan to beinitiated even when the neighboring AP is operating in PCF (PointCoordination Function) and the network is in CFP (Contention FreePeriod), during which unassociated mobile stations (including thescanning mobile station) cannot send packets.

In one embodiment, the mobile station selects a channel of interest,sends a Probe Request for Proxy frame to the current AP, and moves tothe selected channel. The mobile station then determines if any ProbeResponse frame from a neighboring AP is received before a time period(MaxChannelTime) expires. If so, then the mobile station sends an ACKand processes each Probe Response frame received.

For the current AP, upon receipt of the Probe Request for Proxy frame,it examines the neighbor SSID field in the received Probe Request forProxy frame. If the neighbor SSID field has a non-broadcast SSID, thecurrent AP determines if it knows the IP address or addresses of the APor APs that have the specified SSID and operates on the specifiedchannel. If so, the current AP sends a Proxy Probe Request packet to theIP address of each known AP. Otherwise, the current AP sends a ProxyProbe Request packet to the IAPP multicast address for all APs in the DSoperating on the specified channel. If the neighbor SSID field has abroadcast SSID, the current AP determines if the IP address is known forthe APs that operate on the specified channel. If so, the current APsends a Proxy Probe Request packet to the IP address of each known AP.Otherwise, the current AP sends the Proxy Probe Request to the IAPPmulticast address.

Thus, if the current AP has the information on the IP address(es) of theAP(s) to be examined, then it can send the Proxy Probe Request packet(s)only to those AP(s) using, for example, TCP/IP protocol. Otherwise, itcan multicast the packet on the entire DS using IAPP multicast so thatevery AP in the DS can receive and respond if it satisfies theconditions posed by channel, BSSID, and SSID fields.

For the neighboring AP, upon receipt of the Proxy Probe Request packet,the neighboring AP investigates the channel, BSSID, and SSID fields inthe received packet. The neighboring AP responds to the Proxy ProbeRequest packet by sending a Probe Response frame to the mobile stationonly when channel, BSSID, and SSID information matches its own ones.This is why the current AP can multicast Proxy Probe Request frame onthe entire DS when it has no information on the IP address of the APswhich satisfies the condition posed by the three fields. The ProbeResponse frame is transmitted until an ACK is returned from the mobilestation or the RetryLimit is reached. Thus, even when the mobile stationmoves to the operation channel of the AP later than the firsttransmission of the Probe Response frame, it can receive theretransmitted Probe Response frame. This eliminates the burden ofsynchronizing the mobile station's channel tuning activity and theneighbor AP's Probe Response frame.

An additional advantage of this embodiment is that basically all APs inthe DS operating on the specified channel respond to the Probe Requestfor Proxy frame. Thus, the mobile station can obtain all the informationon the neighboring APs in the DS and operating on the channel. Further,the Probe Response frame is delivered directly from the neighboring APsto the mobile station over the channel being examined. This allows theavailability of the AP to be confirmed through actual frame exchanges.

According to another embodiment, the mobile station is interested in aspecific neighboring AP and has the basic information on that AP. Theinformation includes the BSSID and operation channel of the AP. Theactive scan procedure is similar to the active scan procedure in theabove embodiment, except that the mobile station specifies in ProbeRequest for Proxy frame the specific AP to be examined. Only thespecified AP responds, by sending on its operation channel a ProbeResponse frame to the mobile station. As a result, the mobile stationdoes not have to stay on the channel after receiving a Probe Responseframe and sending ACK to the frame. Since the mobile station can fastreturn to the current communication channel, scanning overhead isreduced and the fast handoff is facilitated.

As in the earlier embodiment, the mobile station in this embodiment doesneither have to move to the channel to be examined nor have to send aProbe Request frame on that channel. This enables active scan to be doneeven when the neighbor AP is operating in PCF with long CFP. As in theearlier embodiment, the Probe Response frame in this embodiment isdelivered directly from the neighbor AP to the mobile station over theoperation channel of the AP. Thus, availability of AP is confirmedthrough actual frame exchange.

According to yet another embodiment, a CF-pollable mobile station isinterested in a specific neighboring AP and wants to authenticated.Since the mobile station is allowed to be authenticated with multipleAPs at the same time, it may choose to be authenticated with whicheverAPs are found by the scanning. This allows possible subsequent handoffprocedures to be expedited. The mobile station has the basic informationto specify an AP, such as the BSSID and operation channel of the AP andincludes this information in the Probe Request for Proxy frame tospecify the AP to be examined. In this embodiment, the mobile stationfurther requests CF-Poll from the specified AP. If the specified AP hasPCF that is for polling as well as delivery, and if its pollingschedules permits, the specified AP shall respond by sending on itsoperation channel a Probe Response and CF-Poll frame to the mobilestation. Thus the mobile station can immediately proceed to the step ofauthentication by sending an Authentication and CF-Ack frame. Since themobile station can fast proceed to the authentication step, scanning andauthentication overhead is reduced and the fast handoff is facilitated.

As in the earlier embodiments, the mobile station in this embodimentdoes neither have to move to the channel to be examined nor have to sendProbe Request frame on that channel. This enables active scan andauthentication to be initiated even when the neighboring AP is operatingin PCF with long CFP. In this embodiment, the Probe Response frame andAuthentication frames are delivered directly between the neighbor AP andthe mobile station over the operation channel of the neighboring AP.Thus, availability of AP is confirmed through actual frame exchange.Note that the mobile station can send frames to current AP using eitherDCF or PCF since it is already associated (in contrast, the mobilestation cannot send frames to neighbor AP operating in PCF since it isnot yet associated with the neighboring AP). This embodiment isbasically for investigating the availability and the characteristics ofa specific neighbor AP, but the mobile station also has the intention toauthenticate with the neighboring AP. So the CF-Poll as well as theBSSID of the AP is specified in the frame body of the Probe Request forProxy frame.

With some embodiments, the scanning method used in by explicitindication in the header of the Probe Request for Proxy frame. However,in other embodiments, the explicit indication or notification is withinpredetermined fields in the frame body of an action frame.

The scope of the invention is defined by the claims, which areincorporated into this section by reference. A more completeunderstanding of embodiments of the present invention will be affordedto those skilled in the art, as well as a realization of additionaladvantages thereof, by a consideration of the following detaileddescription of one or more embodiments. Reference will be made to theappended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless network according to oneembodiment;

FIG. 2 shows the format of a management frame according to oneembodiment;

FIG. 3 shows the format of an IAPP packet according to one embodiment;

FIG. 4 is a flow chart showing actions of a mobile station according toone embodiment for the network of FIG. 1;

FIG. 5 is a flow chart showing actions of a current access pointaccording to one embodiment for the network of FIG. 1;

FIG. 6 is a flow chart showing actions of a neighboring access pointaccording to one embodiment for the network of FIG. 1;

FIG. 7 is a flow chart showing actions of a mobile station according toone embodiment when the mobile station knows the basic information for aspecific neighboring AP;

FIG. 8 is a block diagram of a wireless network, according to anotherembodiment, where the mobile station is CF-pollable and interested in aspecific neighboring AP, with authentication by the APs;

FIG. 9 is a flow chart showing actions of a mobile station according toone embodiment for the network of FIG. 8; and

FIGS. 10A and 10B show formats of an action frame and an action framebody, respectively, according to one embodiment.

Embodiments of the present invention and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

According to one aspect of the present invention, an active scanningmethod in a wireless network uses inter-AP (Access Point) communicationfor determining available access points. In the scanning method, amobile station sends a Probe Request for Proxy frame to the current APserving the mobile station. In response to the Probe Request for Proxyframe, the current AP send Proxy Probe Request packet to the appropriateAPs. In response to the Proxy Probe Request packet, the neighbor APssend a Probe Response frame to the mobile station on its operatingchannel. Since the mobile station moves to the channel being examinedafter sending the Probe Request for Proxy frame, the mobile stationreceives the Probe Response frame if the mobile station is in thecoverage area of the neighbor AP. The content of Probe Response frameprovides the mobile station with the information to be used in handoffdecision and network join procedures.

FIG. 1 is a block diagram of a network 100 according to one embodimentof the present invention. Network 100 includes a mobile station 102, acurrent AP 104 in communication with mobile station 102, and aneighboring AP 106. The mobile stations can be any device that canfunction within the 802.11 protocol, e.g., with physical layer (PHY)interfaces to the wireless medium and Media Access Control (MAC) thatutilizes Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) protocol. Examples of suitable devices include laptop PCs andhandheld devices, such as PDAs. These devices can be mobile, portable,or stationary. Network 100 can be an 802.11 conformant network, whichtypically includes a plurality of Basic Service Sets (BSSs), with eachBSS having multiple wireless stations and an AP. Mobile station 102 andAPs 104 and 106 each include an antenna 108 for transmitting andreceiving frames or packets, as will be discussed below, and a processor110 for processing the received information and preparing outboundframes or packets for transmission. Antennas 108 can be different, as isknown, for mobile stations and APs. Further, separate receiving andtransmitting antennas may be used instead of a single antenna 108 forboth receiving and transmitting. Antenna 108 can be part of atransmitter, receiver, or transceiver.

Within network 100, mobile station 102 sends a Probe Request for Proxyframe to current AP 104, for each channel, to find available neighboringAPs, such as AP 106, to learn their characteristics. In response to thisframe, current AP 104 sends a Proxy Probe Request packet to the all APsin the Distribution System (DS). In other embodiments, the packet issent only to the APs operating on the particular channel. Transmissionbetween APs, such as between current AP 104 and neighboring AP 106,utilizes IAPP (Inter-AP Protocol), which is being standardized in theIEEE 802.11 TGf task group, details of which can be found in IEEE Std802f/D5.0, “Draft Recommended Practice for Multi-Vendor Access PointInteroperability via an Inter-Access Point Protocol Across DistributionSystems Supporting IEEE 802.11 Operation”, January 2003, incorporated byreference in its entirety.

IAPP specifies the information to be exchanged between APs amongstthemselves and higher layer management entities to support the 802.11 DSfunctions. IAPP will allow APs to interoperate on a common DS, using theTransmission Control Protocol over IP (TCP/IP) or User Datagram Protocolover IP (UDP/IP) to carry IAPP packets between APs. An IAPP packet iscarried in the TCP or UDP protocols over IP. Other communication schemesmay also be used for transmission of packets between APs.

In response to a Proxy Probe Request packet sent by current AP 104, APsin the DS operating on the channel send a Probe Response frame to themobile station on its operating channel. FIG. 1 shows only neighboringAP 106 sending the Probe Response frame for clarity, although mobilestation 102 may receive Probe Response frames from many different APs.After sending the Probe Request for Proxy frame, mobile station 102moves to the channel being examined. The receipt of Probe Response framefrom an AP, such as neighboring AP 106, teaches the mobile station thatit is in the coverage area of the AP and thus the AP is available. Thecontent of the Probe Response frame, as will be discussed below,provides the mobile station with the information to be used in handoffdecision and network joining procedures.

The Probe Request for Proxy frame sent by mobile station 102 is, inembodiment, a management frame 200 whose frame format is as shown inFIG. 2, with the frame body comprising the fields shown in Table 1below.

TABLE 1 Order Information 1 Channel 2 BSSID 3 SSID 4 MAC address 5Capability information 6 Supported ratesThe Probe Request for Proxy frame has fields as shown in Table 2according to one embodiment.

TABLE 2 Field Value MAC header DA MAC address of current AP SA MACaddress of mobile station Current BSSID MAC address of current AP Framebody Channel Channel to be examined Neighbor BSSID Broadcast BSSIDNeighbor SSID Broadcast SSID or SSID of neighbor AP or APs MAC addressMAC address of mobile station Capability CF-Pollable & CF-Pollinformation Request in Type 1, 2, or 4 given in Table 3 below MAC OthersDetermined as in the header/Frame Probe Request frame body

TABLE 3 CF- CF-Poll Type Pollable Request Meaning 1 0 0 station is notCF-Pollable 2 0 1 station is CF-Pollable, not requesting to be placed onthe CF-Polling list 3 1 0 station is CF-Pollable, requesting to beplaced on the CF-Polling list 4 1 1 station is CF-Pollable, requestingnever to be polledA station that is able to respond to CF-Polls is referred to as beingCF-Pollable and may request to be polled by an active PCF. When polledby the AP, a CF-Pollable station may transmit only one frame and may“piggyback” the acknowledgment of a frame received from the AP usingparticular data frame subtypes with CF-Ack. If the addressed recipientof a CF (Contention Free) transmission is not CF-Pollable, that stationacknowledges the transmission using DCF acknowledgment rules.

The body of a Probe Request frame has two fields: the SSID (Service SetIdentifier) and the rates supported by the mobile station. APs thatreceive Probe Requests use the information to determine whether thestation can join the network. In one embodiment, the mobile station mustsupport all the data rates required by the AP and must want to join anynetwork identified by the SSID. Generally, type bits (B2, B3) andsubtype bits (B4-B7) of the frame control field are used for identifyingthe frame. Any reserved type and subtype bits pair in Table 4 below canbe assigned to a Probe Request for Proxy frame. For example type bits of00 and subtype bits of 1110 can be assigned to Probe Request for Proxyframe.

TABLE 4 Type Subtype Value Type value Subtype B3 B2 description B7 B6 B5B4 description 00 Management 0100 Probe Request 00 Management 0101 ProbeResponse 00 Management 1000 Beacon 00 Management 1101 Action 00Management 1110-1111 Reserved 01 Control 1101 Acknowledgement (ACK)

As discussed above, upon receipt of a Probe Request for Proxy frame,current AP sends a Proxy Probe Request packet to neighboring APs. In oneembodiment, the Proxy Probe Request packet is an IAPP packet 300, asshown in FIG. 3, with the same information for the data fields as theProbe Request frame, shown in Table 1 above. The Proxy Probe Requestpacket is transferred using UDP or TCP/IP protocol, according to oneembodiment. UDP/IP may be desirable if the packet is multicast on theentire DS. In one embodiment, Proxy Probe Request packet has the fieldsfilled in accordance with Table 5.

TABLE 5 Field Value TCP/UDP Port 3517 header IP Destination Multicastaddress header address (224.0.1.178) or IP addresses of individual APsSource IP address of current AP address IAPP Command 7 (as in Table 6below) Data Copied from the frame body of Probe Request for Proxy frame

TABLE 6 Value Command 0 ADD-notify 1 MOVE-notify 2 MOVE-response 3Send-Security-Block 4 ACK-Security-Block 5 CACHE-notify 6 CACHE-response7 Proxy-Probe-Request 8-255 Reserved

After receiving the Proxy Probe Request, a neighboring AP 106 transmitsa Probe Response frame to mobile station 102. This frame, in oneembodiment, is a management frame whose frame format is as shown in FIG.2, with the frame body comprising the fields as shown in Table 7 below.

TABLE 7 Order Information Notes 1 Timestamp 2 Beacon interval 3Capability information 4 SSID 5 Supported rates 6 FH Parameter The FHParameter Set information Set element is present within Probe Responseframes generated by stations using frequency hopping PHYs. 7 DSParameter The DS Parameter Set information Set element is present withinProbe Response frames generated by stations using direct sequence PHYs.8 CF Parameter The CF Parameter Set information Set element is presentwithin Beacon frames generated by APs with an active PCF.The allowed field values for the Probe Response frame, in oneembodiment, are given in Table 8.

TABLE 8 Field Value \ MAC header DA MAC address of mobile station SA MACaddress of neighbor AP BSSID MAC address of neighbor AP MAC OthersDetermined as in header/Frame the normal Probe body Response frame

FIG. 4 is a flow chart 400 showing one embodiment of the presentinvention for a mobile station in proxy active scan. In step 402, mobilestation 102 performs the following: 1) Selects a channel to be examined;2) Performs a medium access procedure (e.g., DCF or PCF) on theoperation channel of current AP 104; 3) Sends a Probe Request for Proxyframe to current AP 104, with the Probe Request for Proxy frame havingthe format and field values as discussed above; 4) Moves to the channelto be examined; and 5) Clears and starts a ProbeTimer. If the medium hasnot been detected busy before the ProbeTimer reaches MinChannelTime, asdetermined in step 404, then the procedure ends (the channel is notoperated by an AP in PCF). If the medium has been detected busy duringthe MinChannelTime, a determination, in step 406, is made whether theProbeTimer has reached MaxChannelTime. Until MaxChannelTime has beenreached, the mobile station acknowledges any received Probe Responseframe, in step 408. Once MaxChannelTime has been reached, all receivedProbe Response frames are processed in step 410.

In one embodiment, MinChannelTime is set to a value long enough todetect a neighboring AP operating PCF on the channel, and MaxChannelTimeis set long enough for the neighboring AP to respond to the ProbeRequest for Proxy frame. The round trip time between the current AP andthe neighboring APs in IAPP as well as processing time and scheduling ofcurrent AP 104 and neighboring AP 106 should be considered. Note thatmobile station 102 can send frames to current AP 104 using either DCF orPCF since the mobile station is already associated. In contrast, mobilestation 102 cannot send frames to neighboring AP 106 operating in PCFsince the mobile station is not yet associated with the neighbor AP. Asdiscussed above, the body of the Probe Request frame contains rate andSSID data. By specifying the desired channel, all APs operating on aspecific channel to be found. If mobile station is only interested inthe APs having a specific SSID among those operating on the channel, onthe other hand, the SSID can be further specified in the frame body.

FIG. 5 is a flow chart showing processing with current AP 104 afterreceiving a Probe Request for Proxy frame from mobile station 102. Instep 502, current AP 104 determines, from the frame body of the ProbeRequest for Proxy frame, whether the neighbor BSSID (Basic Service SetIdentifier) field has the broadcast BSSID, where the neighbor BSSID andneighbor SSID fields in the frame body of the Probe Request for Proxyframe are as shown in Table 2. If so, step 504 determines whether theneighbor SSID field in the frame body of the Probe Request for Proxyframe has the broadcast SSID. If the neighbor SSID has the broadcastSSID, step 506 determines whether the current AP knows the IP address oraddresses of AP or APs operating on the channel specified by the channelfield in the frame body of the Probe Request for Proxy frame. If thecurrent AP knows the IP address or addresses of AP or APs, as determinedin step 506, the current AP sends a Proxy Probe Request packet to theseAP(s) operating on the specified channel at the IP address(es) in step508. Transmission to specific IP address(es) can be performed with theTCP/IP protocol or any other suitable scheme. Otherwise (i.e., thecurrent AP does not know the IP addresses of APs operating on thespecified channel, as determined in step 506), the current AP sends aProxy Probe Request packet to all APs in the DS using an IAPP multicastaddress in step 510.

If, as determined in step 504, the neighbor SSID is different than thebroadcast SSID, the current AP determines, in step 512, whether the IPaddress or addresses of the AP or APs of the specified channel and SSIDare known. If so, the current AP sends, in step 514, a Proxy ProbeRequest packet to the APs operating on the specified channel and havingthe specified SSID. Otherwise, current AP 104 sends the Proxy ProbeRequest packet using an IAPP multicast address in step 510.

Referring back to step 502, if the neighbor BSSID is different than thebroadcast BSSID, the current AP determines, in step 516, whether the IPaddress of the AP having the specified BSSID is known. If the IP addressis known, current AP 104 sends a Proxy Probe Request packet to the APoperating on the specified channel and having the specified BSSID instep 518. However, if the IP address is not known, as determined in step516, current AP 104 transmits a Proxy Probe Request packet using an IAPPmulticast address in step 510.

Thus, if the current AP 104 has the information on the IP address(es) ofthe AP(s) to be examined, then the current AP can send the Proxy ProbeRequest packet(s) to the specific AP(s) using, for example, TCP/IPprotocol. Otherwise, the current AP can multicast the packet on theentire DS using IAPP multicast so that every AP in the DS can receiveand respond if any of the APs in the DS satisfies the conditions posedby channel, BSSID, and SSID fields.

FIG. 6 is a flow chart 600 showing actions, according to one embodiment,for a neighboring AP 106 after the neighboring AP receives a Proxy ProbeRequest from current AP 104, either by unicast (using TCP/IP protocol)or by multicast. Upon reception of the Proxy Probe Request, neighboringAP 106, which can be any neighboring AP in the DS, resets its counter tozero in step 602. Neighboring AP 106 then determines, in step 604,whether the specified channel matches the neighboring AP's operationchannel by using the channel field of the Proxy Probe Request packet(see Tables 1 and 2 above). If yes, neighboring AP 106 uses the SSIDfield of the Proxy Probe Request packet to determine whether thespecified SSID matches its SSID or is the broadcast SSID, in step 606.If there is again a match, the AP determines, in step 608, whether thespecified BSSID matches its own BSSID. If not, a determination is madein step 610 as to whether the specified SSID matches the broadcast SSID.If there is no match in the determinations made in steps 604, 606, or610, the neighboring AP stops processing for that received Proxy ProbeRequest packet.

If the specified BSSID matches the broadcast BSSID, as determined instep 610, the neighboring AP sends a Probe Response frame to the currentor specified mobile station in step 612. If an ACK frame from thespecified mobile station has been received by the neighboring AP,indicating that the mobile station has received the Probe Responseframe, such as in SIFS, or if the counter has reached RetryLimit, asdetermined in step 614, the processing for the current Proxy ProbeRequest packet is ended. However, if an ACK frame was not received andthe counter has not reached RetryLimit, the counter is increased in step616 and another Probe Response frame is sent in step 612. RetryLimit isan adjustable parameter in implementation. When RetryLimit is large,erroneous packet delivery failures can be reduced if the receiver is inthe coverage area but frame retransmission can be just waste of wirelessresource if the receiver is out of coverage area. Most MACs withretransmission capability have similar parameters. The value of theparameter can be same for all kinds of frame transmissions or can bedifferent according to the types.

Returning to step 608, if the specified BSSID matches the BSSID of theneighboring AP, the AP determines if a CF-Poll (type 3) has beenrequested in step 618. If not, the AP sends a Probe Response frame tothe mobile station in step 612 and processing continues as before.However, if a CF-Poll has been requested, the AP transmits a ProbeResponse with CF-Poll frame to the specified mobile station in step 620.If a CF-ACK frame is received by the AP, indicating receipt by themobile station, or the counter has reached RetryLimit, as determined instep 622, the process ends for the current Proxy Probe Request packet.However, if a CF-ACK frame was not received and the counter has notreached RetryLimit, the counter is increased in step 624 and the APsends another Probe Response and CF-Poll frame are sent in step 620.Processing then continues until either a CF-ACK frame is received or thecounter has reached RetryLimit.

The frame format and the field values in the Probe Response frame arebasically the same as in conventional active scanning. A neighboring APresponds to a Proxy Probe Request packet by sending Probe Response frameto the mobile station only when both the neighboring AP and the mobilestation have the same operating channel, BSSID, and SSID. This allowsthe current AP to multicast Proxy Probe Request frames on the entire DSwhen it has no information on the IP address of the APs which satisfiesthe condition posed by the three fields.

It should be noted that even when the neighboring AP is operating PCF,the neighboring AP can send frames to the mobile station that is not yetassociated. However, because the non-associated mobile station is not onthe AP's polling list, the non-associated AP cannot generally sendframes to the AP. Thus, the Probe Response frame is transmitted by theneighboring AP until an ACK is returned from the mobile station or theRetryLimit is reached. Consequently, even when the mobile station movesto the operation channel of the AP later than the first transmission ofthe Probe Response frame, the mobile station can receive theretransmitted Probe Response frame. This eliminates the burden ofsynchronizing the mobile station's channel tuning activity and theneighbor AP's Probe Response frame.

Referring back to FIG. 1, according to another embodiment of the presentinvention, mobile station 102 sends information about a specificneighboring AP in the Probe Request for Proxy frame to its current AP104. The information includes the BSSID and operation channel of theneighboring AP. The active scan procedure is similar to that of theembodiment discussed above. However, because the Probe Request for Proxyframe contains information for a specific neighboring AP, only thespecified AP shall respond by sending on its operation channel a ProbeResponse frame to the mobile station.

The format of Probe Request for Proxy frame is the same as describedabove in FIG. 2 and Table 1. According to one embodiment, the frame hasthe fields filled in accordance with Table 9 below. Values in the fieldthat that are changed from those of Table 2 are shown in bold.

TABLE 9 Field Value MAC header DA MAC address of current AP SA MACaddress of mobile station Current MAC address of BSSID current AP Framebody Channel Operation channel of neighbor AP to be examined NeighborMAC address of BSSID neighbor AP to be examined Neighbor Broadcast SSIDor SSID SSID of neighbor AP to be examined MAC address MAC address ofmobile station Capability CF-Pollable & CF- information Poll Request inType 1, 2, or 4 MAC Others Determined as in header/Frame the ProbeRequest body frameAs seen from Table 9, the Probe Request frame sent by mobile station 102includes the operating channel, BSSID, and SSID information for theselected neighboring AP.

Once the Probe Request frame is received by current AP 104, it transmitsa Proxy Probe Request packet. The format is the same as in theembodiment described above in FIG. 3 and Table 1. The Proxy ProbeRequest packet is transferred using UDP or TCP/IP protocol, in oneembodiment. TCP/IP provides the capability of retransmission if the IPaddress of the specified AP is known. Table 10 below shows fields forthe Proxy Probe Request packet according to one embodiment, with thefield values changed from Table 5 shown in bold.

TABLE 10 Field Value TCP/UDP Port 3517 header IP Destination Multicastaddress header address (224.0.1.178) or IP address of the specificneighbor AP specified in the Probe Request for Proxy frame Source IPaddress of current AP address IAPP Command 7 (as in Table 6) Data Copiedfrom the frame body of Probe Request for Proxy frame

Upon receipt of the Proxy Probe Request, the specified neighboring APtransmits a Probe Response, where the format and field values have thesame format and values as in embodiment discussed above.

FIG. 7 is a flow chart 700 showing the steps performed by mobile station102 according to one embodiment when the mobile station knows the basicinformation for a specific neighboring AP. In step 702, mobile station102 performs the following: 1) selects an AP to be examined; 2) performsthe medium access procedure (DCF or PCF) on the operation channel of thecurrent AP; 3) sends a Probe Request for Proxy frame to current AP 104,with the Probe Request for Proxy frame having the format and fieldvalues as described above; 4) moves to the operation channel of the APto be examined, and 5) clears and starts a ProbeTimer.

A determination is then made in step 704 as to whether the medium hasbeen detected busy before ProbeTimer reaches MinChannelTime. If not,then the procedure ends (i.e., the channel is not operated by an AP inPCF). However, if the medium has been detected busy, the mobile stationdetermines, in step 706, whether ProbeTimer has reached MaxChannelTime.If it has, the procedure ends. If ProbeTimer has not reachedMaxChannelTime, a determination is made in step 708 whether a ProbeResponse frame was received by the mobile station. If not, ProbeTimer ischecked again, in step 706. Thus, if the Probe Response frame is notreceived before ProbeTimer reaches MaxChannelTime, then the procedureends (i.e., the channel is operated by an AP that is not reachableeither by current AP through IAPP or by mobile station through air). Ifa Probe Response frame is received from the selected neighboring AP, themobile station sends an ACK and processes the received Probe Responseframe in step 710.

As in the embodiments of FIGS. 4-6, MinChannelTime is set to a valuelong enough to detect a neighboring AP operating PCF on the channel, andMaxChannelTime is set long enough for the neighboring AP to respond tothe Probe Request for Proxy frame. Round trip time between the currentAP and neighboring APs in IAPP as well as processing time and schedulingof current AP and neighboring AP should be considered. Similarly, themobile station can send frames to the current AP using either DCF or PCFsince the mobile station is already associated (in contrast, the mobilestation cannot send frames to a neighboring AP operating in PCF since itis not yet associated with the neighbor AP).

Referring to FIG. 5, once the current AP receives the Probe Request forProxy, the current AP uses the BSSID of the specified AP in the(neighbor) BSSID field of the frame body in the Probe Request for Proxyframe. Current AP 104 determines if the IP address is known for the APhaving the specified BSSID and operating on the specified channel. Ifso, current AP 104 transmits a Proxy Probe Request packet to the IPaddress of the AP, such as by TCP/IP protocol. However, if the addressis not known, current AP 104 multicasts the packet on the entire DSusing IAPP multicast so that every AP in the DS can receive and respondif it satisfies the conditions posed by the channel, BSSID, and SSIDfields.

Referring now to FIG. 6, once the specified neighboring AP receives aProxy Probe Request packet from the current AP, the neighboring APinvestigates the frame's channel, Neighbor BSSID, Neighbor SSID,capability information fields. If the BSSID specified in the BSSID fieldmatches its own BSSID and CF-Poll is not requested (type 1, 2, or 4) inthe capability information field, the neighboring AP uses the sameprocedure as described in FIG. 6.

As with the previous embodiment of FIGS. 4-6, even when the neighboringAP is operating PCF, it can send frames to the mobile station that isnot yet associated. A Probe Response frame is transmitted until an ACKis returned from the mobile station or the RetryLimit is reached. Thus,even when the mobile station moves to the operation channel of the APlater than the first transmission of the Probe Response frame, it canreceive the retransmitted Probe Response frame.

As a result, the mobile station advantageously does not have to stay onthe channel after receiving a Probe Response frame and sending an ACK inresponse to the frame. Since the mobile station can fast return to thecurrent communication channel, scanning overhead is reduced, and thefast handoff is facilitated. Further, as with the earlier embodiment,the mobile station neither has to move to the channel to be examined norhas to send a Probe Request frame on that channel. This enables activescan to be done even when the neighboring AP is operating in PCF withlong CFP. Similarly, the Probe Response frame is delivered directly fromthe neighboring AP to the mobile station over the operation channel ofthe AP. Thus, the availability of the AP is confirmed through actualframe exchange.

FIG. 8 shows another embodiment of the present invention, in which anetwork 800 includes communication between a mobile station 802, acurrent AP 804, and a neighboring AP 806, as with FIG. 1. As with FIG.1, the mobile station and the APs have antennas 808 for transmitting andreceiving packets or frames, and a processor 810 for processing thereceiving information and preparing outgoing packets or frames fortransmission. Note also that although only one neighboring AP 106(FIG. 1) or 806 (FIG. 8) is shown, the invention is not limited to onlyone, but can have multiple neighboring APs, as is obvious from thedescription contained herein. However, in this embodiment, mobilestation 802 is CF-pollable and is interested in a specific neighboringAP, with authentication by the APs. Since mobile station 802 is allowedto be authenticated with multiple APs at the same time, it may choose tobe authenticated with whichever APs found by the scanning. This is toexpedite possible handoff procedures which may happen later. The activescanning by mobile station 802 is similar to that of the embodimentdescribed above with reference to FIG. 7.

The format of the Probe Request for Proxy frame transmitted by mobilestation 802 is the same as described above with reference to FIG. 2 andTable 1. Table 11 below shows fields for the Probe Request for Proxyframe, according to one embodiment, where the field values differingfrom Table 9 are shown in bold.

TABLE 11 Field Value MAC header DA MAC address of current AP SA MACaddress of mobile station Current MAC address of BSSID current AP Framebody Channel Operation channel of neighbor AP to be examined NeighborMAC address of BSSID neighbor AP to be examined Neighbor Broadcast SSIDor SSID SSID of neighbor AP to be examined MAC address MAC address ofmobile station Capability CF-Pollable & CF- information Poll Request inType 3 MAC Others Determined as in header/Frame the Probe Request bodyframe

The format and field values for the Proxy Probe Request packet sent bycurrent AP 804 and for the Probe Response frame sent by neighboring AP806 are the same as those described above for the embodiment of FIG. 7.

FIG. 9 is a flowchart 900 showing actions of mobile station 802according to one embodiment. In step 902, mobile station 802 performsthe following: 1) selects an AP to be examined; 2) performs the mediumaccess procedure (DCF or PCF) on the operation channel of the currentAP; 3) sends a Probe Request for Proxy frame to current AP 804, with theProbe Request for Proxy frame having the format and field valuesdescribed above; 4) moves to the operation channel of the AP to beexamined; and 5) clears and starts a ProbeTimer. Next, in step 904,mobile station 802 determines if the medium has been detected busybefore the ProbeTimer reaches MinChannelTime. If not, then the procedureends (i.e., the channel is not operated by an AP in PCF).

However, if the medium has been detected busy, mobile station 802determines, in steps 906 and 908, whether the ProbeTimer has reachedMaxChannelTime before receiving a Probe Response frame. If so, then theprocedure ends (i.e., the channel is operated by an AP that is notreachable either by current AP through IAPP or by mobile station throughair). If a Probe Response frame is received before the ProbeTimerreaches MaxChannelTime, the received frame is processed to determine ifthe frame has CF-Poll, in step 910. If the frame does not have CF-Poll,mobile station 802 sends an ACK for the received Probe Response frameand processes the Probe Response frame in step 912. However, if theProbe Response frame has CF-Poll, mobile station 802, in step 914,processes the Probe Response frame, sends an Authentication frame with aCF-Ack, and performs a subsequent authentication procedure.

As in the above described embodiments, MinChannelTime and MaxChannelTimeare set to the appropriate values. Likewise, the mobile station can sendframes to the current AP using either DCF or PCF since the mobilestation is already associated (in contrast, the mobile station cannotsend frames to neighbor AP operating in PCF since it is not yetassociated with the neighbor AP). As with the embodiment of FIG. 7, thisembodiment is basically for investigating the availability and thecharacteristics of a specific neighbor AP, but the mobile station inthis embodiment also has the intention to authenticate with the neighborAP. So the CF-Poll, as well as the BSSID of the AP, is specified in theframe body of the Probe Request for Proxy frame.

The procedure of current AP 804 in this embodiment is the same as withthe current AP in the embodiment described above with reference to FIG.7.

The procedure of neighboring AP 806 is now described with reference toFIG. 6, with some distinctions, as will be noted. After receiving aProxy Probe Request packet from current AP 804, neighboring AP 806investigates the packet frame's channel, Neighbor BSSID, Neighbor SSID,and capability information fields. The neighboring AP responds to theProxy Probe Request only when the BSSID specified in the BSSID fieldmatches the BSSID of the neighboring AP (see, e.g., step 608). IfCF-Poll is requested in the capability information field (type 3) of theProxy Probe Request packet (see, e.g., step 618), a change from FIG. 6is that the neighboring AP next determines whether it has PCF that isfor polling, and if its polling schedule permits the CF-Poll to themobile station.

In doing so, the effect on QoS (Quality of Service) of other mobilestations will also be considered. Specifically, CF-Poll may be allowedonly when the consecutive frame transmissions allowed by CF-Poll do notdeteriorate QoS of other mobile stations. If the CF-Poll is permissibleas a result of the consideration, the neighboring AP responds by sendingon its operation channel a Probe Response with CF-Poll frame to themobile station (see, e.g., step 620). If the CF-Poll is not permissible,the neighboring AP responds by sending simply a Probe Response (that is,without CF-Poll). If the Probe Response with CF-Poll frame is sent,mobile station 802 can immediately proceed to the step of authenticationby sending an Authentication with CF-Ack frame back to neighboring AP806. Since the mobile station can fast proceed to the authenticationstep, scanning and authentication overhead is reduced, and the fasthandoff is facilitated.

It should be noted that the CF-Poll with Probe Response transmission isdone only in response to a Proxy Probe Request and is temporary innature. Otherwise, the neighboring AP will continue to poll the mobilestation even after it finishes the scanning procedure and returns to itsoriginal channel, which leads to significant waste of bandwidth for theneighboring AP. In these aspects, the CF-Poll with Probe Response isdifferent from the ordinary CF-Poll that is done for CF-Pollable mobilestations associated with the AP.

Further, as with the embodiments of FIGS. 4-6 and 7, the mobile stationin this embodiment neither has to move to the channel to be examined norhas to send a Probe Request frame on that channel. This enables activescan and authentication to be initiated even when the neighboring AP isoperating in PCF with long CFP. In this embodiment, the Probe Responseframe and Authentication frames are delivered directly between theneighboring AP and the mobile station over the operation channel of theneighboring AP. As a result, availability of the AP is confirmed throughactual frame exchange.

In another embodiment of the invention, the mobile station identifies,from an action frame, the type of scanning method used. As distinguishedfrom the earlier embodiments, where scanning methods are indicated inthe header of Probe Request for Proxy frame, this embodiment usespredetermined fields in the frame body of the action frame (type bits of00 and subtype bits of 1101 in frame control field) for explicitnotification of the scanning method.

An action frame 1000, shown in FIG. 10A, is a type of management frame,like a Probe Request or Probe Response frame. Action frame 1000 includesa MAC header portion 1002, a frame body portion 1004, and a Frame CheckSequence (FCS) 1006. The MAC header and FCS fields are conventional andwell known. The frame body for an action frame includes a Category field1008 and an Action Details field 1010. The action frame provides amechanism for specifying extended management actions, details of whichcan be found in IEEE Std 802.11k/D0.1, “Specification for Radio ResourceMeasurement (Draft Supplement to IEEE Std 802.11, 1999 Edition)”, March2003, which is incorporated by reference in its entirety. The format ofaction frame body 1004 is shown in FIG. 10B, where the Category field isone octet and the Action Details field is a variable number N octets.The Category field is set to one of the non-reserved values shown inTable 12 below.

TABLE 12 Name Value Reserved 0 QoS management 1 DLP 2 Radio measurement3 Reserved  4-127 Error 128-255In this embodiment, any reserved category values can be used toexplicitly indicate the specific proxy active scanning to be used. Forexample, category value of 4 is assigned to indicate the proxy activescanning according to the embodiment of FIGS. 4-6, while category valueof 2 is assigned to indicate the active scanning of the embodiment ofFIG. 7.

The Action Details field contains the details of the action. The detailsof the actions allowed in each category are described in “Specificationfor Radio Resource Measurement (Draft Supplement to IEEE Std 802.11,1999 Edition)”, referenced above. In the radio measurement category, anaction field, in the octet field immediately after the category field,differentiates the specific radio measurement actions. The action fieldvalues are shown in Table 13 below, according to one embodiment.

TABLE 13 Action field value Description 0 Measurement Request 1Measurement Report 2-255 ReservedAny reserved action field values of radio measurement category (categoryvalue of 3) can be used to explicitly indicate the specific activescanning to be used. For example, action field value of 4 is assigned toindicate the active scanning according to the embodiment of FIG. 7,while action field value of 5 is assigned to indicate the activescanning of the embodiment of FIGS. 8 and 9. This embodiment showsvariations in the means for indicating probe request for proxy frame. Itcan be done by an indication either in the header or in the frame body.Indication in the header might be more efficient in view of processingbut would require more changes from the existing implementation.

Embodiments described above illustrate but do not limit the invention.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the present invention.For example, although this invention is explained with respect to activescan, authentication and (re-)association will have the same problem asin the active scanning if the interested AP is operating PCF. So, theuse of the current AP as a proxy to deliver the request to initiateauthentication and (re-)association will similarly solve the problem.These kinds of variations are also within the scope of the invention.Further, although a specific format is shown for a Probe Request forProxy frame and a Proxy Probe Request packet, the present invention isnot constrained by the specific frame and packet format, as othersuitable frame and packet formats may be used. Also, the abovedescription is with reference to IEEE 802.11; however, the invention canbe applied to other types of wireless communication systems.Accordingly, the scope of the invention is defined only by the followingclaims. Although the embodiments are illustrated with reference to thecase where current AP and neighboring APs are in the same DS, theinvention can be easily extended to more general cases where the APs aredifferent DSs.

1. A method of wireless communication, comprising: receiving amanagement request for proxy packet from a mobile station to a currentaccess point (AP), wherein the management request for proxy packetspecifies a channel and a broadcast SSID or BSSID of a neighboring AP ina distributed system; in response to receipt of the management requestfor proxy packet, transmitting a proxy management request packet fromthe current AP to all APs in the distributed system (DS); and inresponse to receipt of the proxy management request packet, transmittinga management response packet from each AP in the DS operating on thespecified channel to the mobile station.
 2. The method of claim 1,wherein transmitting the proxy management request packet is by Inter-APProtocol (IAPP).
 3. The method of claim 1, wherein transmitting theproxy management request packet is by Transport Control Protocol(TCP)/Internet Protocol (IP).
 4. The method of claim 3, furthercomprising identifying the IP address of the neighboring AP.
 5. Themethod of claim 1, further comprising requiring the mobile station tocommunicate on the channel identified in the management request forproxy packet after transmitting the management request for proxy packet.6. The method of claim 1, further comprising using the information inthe management response packet to join the network comprising theneighboring AP.
 7. The method of claim 1, wherein each AP in thedistributed system operating on the specified channel transmits themanagement response packet on the channel identified in the managementrequest for proxy packet.
 8. The method of claim 1, wherein theneighboring AP is operating in Point Coordination Function (PCF).
 9. Themethod of claim 1, wherein the management request for proxy packet is aProbe Request for proxy packet, the proxy management request packet is aproxy Probe Request packet, and the management response packet is aprobe Response packet.
 10. The method of claim 1, further comprisingconfirming the availability of the neighboring AP through a frameexchange.
 11. The method of claim 1, wherein the proxy managementrequest packet comprises a multicast address or an IP address for theneighboring AP.
 12. The method of claim 1, wherein the managementrequest for proxy packet further comprises a CF-Poll Request.
 13. Themethod of claim 12, further comprising transmitting on the operatingchannel information for a CF-Poll from the neighboring AP to the mobilestation.
 14. The method of claim 13, further comprising authenticatingby the mobile station upon receipt of the CF-Poll information.
 15. Themethod of claim 14, wherein the authenticating comprises sending anauthentication and CF-Ack frame from the mobile station to theneighboring AP.
 16. The method of claim 1, wherein the mobile stationneither has to move to the channel nor send a Probe Request frame on thechannel so that active scanning can be initiated when the neighboring APis operating in PCF and the network is in CFP.
 17. The method of claim1, further comprising communicating with at least one other neighboringAP from among the APs in the distributed system operating on thespecified channel, wherein the mobile station can obtain information onall APs in the network and operating on the channel so that the mobilestation can be confirmed through actual frame exchanges.
 18. A method ofwireless communication, comprising: receiving a management request forproxy packet from a mobile station to a current access point (AP),wherein the management request for proxy packet specifies a channel anda broadcast SSID or BSSID of a neighboring AP in a distributed system;in response to receipt of the management request for proxy packet,transmitting a proxy management request packet to all APs in thedistributed system (DS) on the specified channel for which the currentAP has no IP address information on and which match the broadcast SSIDor BSSID; and transmitting a management response packet from each APreceiving the proxy management request packet.
 19. A wirelesscommunication system, comprising: a mobile station; a current accesspoint (AP) configured to receive a management request for proxy packetfrom the mobile station, the management request for proxy packetspecifying a channel and a broadcast SSID or BSSID, and to transmit aproxy management request packet to all APs in a distributed system (DS),in response to the management request for proxy packet; and aneighboring AP configured to receive the proxy management request packetand transmit a management response packet on the channel to the mobilestation in response to the proxy management request packet.
 20. Thesystem of claim 19, wherein the mobile station neither has to move tothe operating channel nor send a Probe Request frame on the channel sothat active scanning can be initiated when the neighboring AP isoperating in PCF and the system is in CFP.
 21. The system of claim 19,further comprising at least a second neighboring AP, wherein the mobilestation can obtain information on all APs in the system and operating ona channel so that the mobile station can be confirmed through actualframe exchanges.
 22. A method of wireless communication at a mobilestation between the mobile station and a neighboring access point (AP),comprising: transmitting a management request for proxy packet to acurrent AP, wherein the management request for proxy packet specifies achannel and a broadcast SSID or BSSID of the neighboring AP; receiving amanagement response packet from the neighboring AP, wherein theneighboring AP transmits the management response packet in response to aproxy management request packet received from the current AP, whichsends the proxy management request packet to all APs in a distributedsystem (DS); and establishing a communication link with the neighboringAP based on information contained in the management response packet. 23.A method of wireless communication between a mobile station and aneighboring access point (AP), the mobile station being associated witha current access point, comprising: receiving, by the neighboring AP, aproxy management request packet from a current AP, wherein the proxymanagement request is sent to all APs on a channel in a distributedsystem (DS) from the current access point in response to a managementrequest for proxy packet sent by the mobile station, the managementrequest for proxy packet specifying the channel and a broadcast SSID orBSSID of the neighboring AP; transmitting a management response packetby the neighboring AP to the mobile station in response to the proxymanagement request packet; and establishing a communication channelbetween the neighboring AP and the mobile station based on infoiniationcontained in the management response packet.
 24. An access point (AP)for use in a wireless communication network, comprising: a receiver forreceiving a management request for proxy packet from a mobile station,wherein the management request for proxy packet specifies a channel anda broadcast SSID or BSSID of a neighboring AP; a transmitter fortransmitting a proxy management request packet to all APs in adistributed system (DS) such that at least one of the APs in thedistributed system transmits a management response packet on thechannel; and a processor for processing information from the managementrequest for proxy packet and the proxy management request packet. 25.The access point of claim 24, wherein the transmitter and the receivercomprise a single transceiver.
 26. The access point of claim 24, whereinthe transmitter comprises a first antenna and the receiver comprises asecond antenna.
 27. The access point of claim 24, wherein the mobilestation neither has to move to the operating channel nor send a ProbeRequest frame on the channel so that active scanning can be initiatedwhen the neighboring AP is operating in PCF and the network is in CFP.28. An access point (AP) for use in a wireless communication network,comprising: a receiver for receiving a proxy management request packetfrom a current AP, wherein the proxy management request is sent on achannel to all APs in a distributed system (DS) from the current AP inresponse to a management request for proxy packet sent by a mobilestation that specifies the channel and a broadcast SSID or BSSID of theneighboring AP; a transmitter for transmitting a management responsepacket to a mobile station in response to the proxy management requestpacket; and a processor for processing information from the proxymanagement request packet and the management response packet.
 29. Theaccess point of claim 28, wherein the transmitter and the receivercomprise a single transceiver.
 30. The access point of claim 28, whereinthe transmitter comprises a first antenna and the receiver comprises asecond antenna.
 31. The access point of claim 28, wherein the mobilestation neither has to move to the operating channel nor send a ProbeRequest frame on the channel so that active scanning can be initiatedwhen the AP is operating in PCF and the network is in CFP.